An electrostatic chuck may be utilized to secure a workpiece using electrostatic forces. The electrostatic chuck may be utilized in various systems such as in an ion implanter. In one instance, the ion implanter may be used to introduce conductivity-altering impurities into a workpiece such as a semiconductor wafer. A desired impurity material may be ionized in an ion source, the ions may be accelerated to form an ion beam of prescribed energy, and the ion beam may be directed at a front surface of the wafer. The energetic ions in the beam penetrate into the bulk of the semiconductor material and are embedded into the crystalline lattice of the semiconductor material to form a region of desired conductivity. The ion beam may be distributed over the wafer area by beam scanning, by wafer movement, or by a combination of beam scanning and wafer movement.
During different time interval the electrostatic chuck may not support any workpiece. An associated control system may sense this condition and cause translation of the electrostatic chuck to a parked position out of the ion beam's trajectory. When the electrostatic chuck is in this parked position, an ion beam may still be generated and directed at a beam stop. This may occur when an operator of the ion implanter runs tests such as extended beam stability tests. This may also occur during ion beam tuning procedures. For these and other reasons, particles may develop and form deposits on the electrostatic chuck when in the parked position. These deposits may adversely affect performance of the electrostatic chuck. For instance, the electrostatic chuck should provide sufficient clamping force to firmly clamp the workpiece to the electrostatic chuck and should be able to quickly clamp and release the workpiece to maintain throughput requirements. Such performance criteria may be adversely affected by particle deposits on the front surface of the electrostatic chuck leading to inconsistent and improper clamping and eventual failure of the electrostatic chuck.
One conventional solution to such particle deposits is to increase the frequency of cleaning of the electrostatic chuck. Drawbacks with this approach include the additional time and expense for such maintenance. In addition, the front surface of the electrostatic chuck may be made of fragile material which makes conventional cleaning methods difficult and may not result in acceptable electrostatic chuck performance even after conventional cleaning. Yet another conventional solution is to replace the entire electrostatic chuck. Drawbacks with this solution include the great expense of replacement in addition to the down time necessary to make such a replacement.
Accordingly, there is a need in the art for an electrostatic chuck to limit deposits thereon when the electrostatic chuck is not supporting any workpiece.